Describe a little better how the machine reacts as you go in reverse. Does it operate correctly as long as the 1A switch is not activated? Once you floor it and activate the 1A switch what happens? When it is jerking, is the reverse contactor chattering on and off? Is the 1A contactor doing anything? The PMTD, HMD, and 1AD are all working OK in forward so it rules them out.
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